A sheet cutting device of this type includes a fixed blade unit and a movable blade unit. The fixed blade unit includes a fixed blade, a fixed blade support device for supporting the fixed blade in a rockable manner, and biasing means for pressurizing the fixed blade against a movable blade. On the other hand, the movable blade unit includes the movable blade, and drive means that is connected to a drive source and drives the movable blade in a stroke direction. Inside a printer, the fixed blade and the movable blade are arranged opposed to each other across front and back surfaces of a sheet that has undergone printing in a sheet passage.
A specific example of the sheet cutting device including a fixed blade support device is disclosed in, for example, Related Art Document 1 of this invention (Japanese Unexamined Patent Application Publication (JP-A) 2001-347485). Referring to FIGS. 1A and 1B illustrating merely a main part of a sheet cutting device similar to that disclosed in Related Art Document 1, the sheet cutting device includes a fixed blade 62, a movable blade 22 driven by drive means (not shown), a fixed blade support member 61 for supporting the fixed blade 62 in a rockable manner, and biasing means (not shown) for pressurizing the fixed blade 62 against the movable blade 22. In order to achieve an operation utilizing the principle of scissors described later, the fixed blade 62 is curved so that its center is protruded toward the movable blade 22, while the movable blade 22 includes a V-shaped blade edge portion and is driven in a stroke direction K. Note that, in some drawings including FIGS. 1A and 1B attached to this specification, for the sake of easy understanding of the description, the sizes and shapes of respective members are schematically illustrated in an exaggerated manner.
This sheet cutting device operates as follows. A sheet (not shown) conveyed between the fixed blade 62 and the movable blade 22 is temporarily stopped, and the drive means causes the movable blade 22 to move in the stroke direction K. The movable blade 22 includes the V-shaped blade edge portion, while the fixed blade 62 is curved toward the movable blade 22 and is provided in a press-contact (engagement) state to the movable blade 22 by the biasing means. Thus, the sheet is cut by the principle of scissors. The cut sheet is delivered from a printer (not shown).
Note that, as the degree of the curve of the fixed blade 62 becomes larger, paper powder is prevented from being generated, but the load on the drive means for the movable blade 22 increases. Therefore, the degree of the curve of the fixed blade 62 is designed considering the balance between reduction of the paper powder and relaxation of the load on the drive means.
As illustrated in FIGS. 2A and 2B, the fixed blade 62 is biased by biasing means 63 in a direction toward the movable blade 22. In this case, at both ends of the fixed blade 62 in a blade width direction in a root portion on the opposite side to a blade edge portion, protruding portions 62b are formed. On the other hand, the fixed blade support member 61 includes rectangle-hole shaped support hole portions 61c into which the protruding portions 62b of the fixed blade 62 are inserted. Each of the protruding portions 62b of the fixed blade 62 is loosely fitted to the support hole portion 61c of the fixed blade support member 61 so that the fixed blade 62 is supported by the fixed blade support member 61 in a rockable manner with the support hole portion 61c as a fulcrum. Note that, the loose fitting of the protruding portion 62b to the support hole portion 61c also acts to prevent the fixed blade 62 biased by the biasing means 63 from being disengaged from the fixed blade support member 61.
In the sheet cutting device illustrated in FIGS. 1A, 1B, 2A, and 2B, the fixed blade 62 is supported by the fixed blade support member 61 in a rockable manner, but in the actual case, the protruding portion 62b itself serving as the rocking fulcrum of the fixed blade 62 is also displaced at the time of engagement between the fixed blade 62 and the movable blade 22. That is, as the engagement of the movable blade (not shown) from the upper side of the figure with respect to the fixed blade 62 progresses as illustrated in FIG. 3B from an initial stage at which the movable blade starts engagement from the upper side with respect to the fixed blade 62 as illustrated in FIG. 3A, the fixed blade 62 rocks toward the lower side of the figure, and the protruding portion 62b of the fixed blade 62 is also displaced toward the lower side of the figure in the support hole portion 61c of the fixed blade support member 61.
However, in the support hole portion 61c of the fixed blade support member 61, the rectangle hole dimensions thereof, that is, positions of the hole wall surfaces in the horizontal direction and the vertical direction in the figure are defined, and hence when the engagement of the movable blade with respect to the fixed blade 62 progresses as illustrated in FIG. 3B, the protruding portion 62b of the fixed blade 62 abuts against the hole wall surface of the support hole portion 61c of the fixed blade support member 61, and thus the room for the press-contact force of the movable blade to escape is eliminated. As a result, the fixed blade 62 having the appropriately designed degree of curve as described above is flattened (the curve degree is reduced). In this case, the normal cutting operation of the sheet cutting device utilizing the principle of scissors is inhibited, and the generation amount of paper powder increases, which are not preferred.